Intimidated Beginner Daunting To Animate
Doubtless this sort of intro question has been answered elsewhere, but briefly - 

Press CTL-SHIFT-Down arrow to reset the timeline to frame 1.  This should be the default anyway.

With the cursor resting on the cube, select it with right mouse button.

Drag the cube to the left and near the edge of the grid.  

Press 'i' and select "Location".  This will register (keyframe) it's location at frame 1.
It means that no matter where the cube is later, returning the timeline cursor to frame 1 will pull the cube back to this same spot.

With your cursor in the timeline at bottom, left click on frame 40. That will take the timeline cursor to this frame.  You can use the left/right arrow keys to manually step frame by frame.

Select the cube again and drag it to the right this time, to the other side of the grid.

Press i once more, choose 'Location'.

This registers (keyframes) the cube's new location for frame 40.  As with the first keyframe, it guarantees the cube will be pulled to this same location whenever the timeline reaches frame 40.

press CTL-SH-Down arrow to reset the timeline to frame 1. (or drag it there in the timeline)

Press the play/stop icons below to see the result, or use the shortcut keys - ALT-A to play the animation.  Press this combo again to make it stop.

You'll see the cube slide from one side of the grid to the other.

There are a stack of Youtube videos that take you through basics such as this.  Just search for "Blender Animation"  or perhaps - "Blender Basic Animation"

Ball bouncing as mentioned in your query is easiest using the physics engine but get used to animating manually first.

You can rotate and scale the cube the same way as you did to make it slide.  Just choose the desired effect when pressing 'i'.

If you get stuck, just leave a comment at the bottom of this answer.

Happy Blending -